Southwestern Speckled Rattlesnake (Crotalus pyrrhus) | Flickr
The Southwestern Speckled Rattlesnake exhibits great variability throughout their range. Their coloration generally matches the tones of the rocks found within their habitat. This, the white variant, lives in an area where the granite is light in coloration with dark flecking.
Reminds me of the time I attempted to backpack in Kings Canyon national park when it happened to be on fire on one end, and I encountered the most rattlesnakes in my life. I hiked in California for the first 20 years of my life and crossed paths with snakes on semi regular occasion, but on this one trip we heard/saw six rattlesnakes in two days, all within striking distance of the trail. Really took the "relax and enjoy the trail" aspect away